1. Field of the Invention
The present invention relates to an electrophotographic recording apparatus, and more particularly to such a scheme of apparatus that light emitting elements such as light emitting diodes (hereinafter referred to as LED) are arranged at intervals of plural dots, and are reciprocatively moved along the arrangement direction.
2. Description of the Prior Art
Such type of electrophotographic recording apparatus is disclosed, for example, in the Japanese Utility Model Application Laid Open No. 58-58553. According to the conventional such apparatuses, it is possible to reduce the number of light emitting elements and the associated driver circuits by reciprocatively moving an array in which LED's are integrated every other dot. On the other hand, according to most prior arts, a photoconductor is driven on a step basis, and the light emitting elements radiate while vibrating in a state that the photoconductor is stopped. However, it is difficult to rotate stepwise the photoconductor, since the photoconductor is usually extremely large in mass, and thus the photoconductor hinders in higher speed. Further, there is such a problem that rotation and stopping operations of the photoconductor invite non-uniform thickness of a toner layer and thus produce uneven printing density.
On the other hand, according to the Japanese Utility Model Application Laid Open No. 58-58553, the photoconductor is rotated at a constant speed. However, this prior art has such a drawback that a right-hand lowered (or left-hand lowered) line is formed, since a latent image point lowers as the photoconductor moves. This drawback is not a problem in a case where the LED's are arranged every other dot. However, when intervals of the light emitting elements are expanded, or when a rotation velocity of the photoconductor is increased, the latent image points, which are essentially to be formed with a straight line, become an oblique line. Thus, this drawback is a problem in a case where fonts or figures are formed.
As one solution for solving the foregoing problem, there is known the Japanese Patent Application Laid Open No. 62-140859. In this prior art, it is stated that in case of a constant rotation of a photoconductor drum, a LED array module is vibrated with a slight slant in an axis direction so as to obtain a coincidence between a rotation velocity of the photoconductor drum and a photoconductor drum rotational direction component of a transfer velocity of the LED array module. This scheme makes it possible to accurately write a row of dots into the photoconductor drum rotating at a constant speed, when the light emitting elements emit light while vibrating once.
However, according to the scheme in which the LED array module is vibrated with a slant in its entirety, as disclosed in the Japanese Patent Application Laid Open No. 62-140859, the ratio of a velocity of the photoconductor in a moving direction to a velocity of the photoconductor in a direction perpendicular to the moving direction is determined on a univocal basis by an angle of inclination of a guide. Thus, for instance, when the light emitting elements are moved in one direction, it is possible to form a line in a cross direction. However, when the light emitting elements are moved in the opposite direction, the line is formed with a skew. Consequently, the conventional scheme simply permits a printing in a single direction.
Moreover, according to the conventional apparatus as disclosed in the Japanese Utility Model Application Laid Open No. 58-58553, it is difficult to reduce a chip area, since such an apparatus is so arranged that a number of LED's are accommodated into a single chip to form an array. As well known by ones skilled in the art, in order to lower a manufacturing cost of a semiconductor, it is important to reduce the chip area. However, such a prior art fails to consider this point, and thus makes impossible the extreme lowering of the manufacturing cost. Further, in the conventional apparatus, there is such a drawback that it is obliged to replace the chip in its entirety even if only a piece of light emitting element in the chip is damaged. Moreover, a large number of chips are needed for a line of printing. Usually, an irregularity in emission intensity is rare within a chip, but it is large in comparison between the chips. This is a problem. In order to solve this problem, there are needs to add a correction circuit on each chip or to selectively use chips which are almost the same in emission intensity. These needs would increase the manufacturing cost. Furthermore, in a case where the chips are disposed on an alignment basis, there will be formed gaps between the adjacent chips, and thus there is a need to provide the chips with a staggered arrangement. This need brings not only an enlargement of a carriage which is loaded with the light emitting elements, but also an increment in weight of the carriage. Thus, it is necessary to use an expensive driving motor of high potential capacity.